The present invention is directed to a monitoring system for determining the magnitudes of the equivalent voltage source impedance and the equivalent voltage source voltage on a telephone line and in particular to a monitoring system for determining and indicating the magnitudes of the equivalent voltage source impedance and the equivalent voltage source voltage in a telephone system of the type having telephone lines and a switching network, wherein operating voltage sources are maintained on the line to support telephone communication and wherein each line and the network combine to form an equivalent voltage source and an equivalent voltage source impedance.
In telephone systems harmful conditions may exist on the telephone lines which could interfere with or interrupt telephone communication. Such conditions may exist on the telephone lines themselves or within the switching network to which the telephone lines are coupled. Such harmful conditions could be foreign potentials due to non-current limited DC potentials or high AC potentials which are greater than or equal to 120 volts AC from the 60 hertz commercial power network. Irregular conditions which also could interfere with telephone communication can be the presence of relatively low resistance leakage paths to ground, or low resistance paths to ground due to relays within the switching network that have not disconnected at the proper time.
It is therefore advantageous to detect such harmful conditions to eliminate the problems which they cause before telephone service is interrupted. The present invention provides a means by which such harmful conditions may be detected by realizing that each telephone line and the network combine to form a Thevenin equivalent voltage source and equivalent voltage source impedance. By measuring the magnitudes of the equivalent voltage source voltage and the equivalent voltage source impedance, such harmful conditions may be detected. It would also be advantageous to perform such a measurement and to convert the result of the measurement to a digital format which is compatable with the network controllers utilized in such telephone systems.
It is therefore a general object of the present invention to provide a monitoring system for measuring and indicating the magnitudes of the equivalent source voltage and equivalent voltage source impedance on a telephone line to detect harmful conditions which may interrupt telephone service.
It is a more particular object of the present invention to provide a monitoring system which measures the magnitudes of the equivalent voltage source voltage and equivalent voltage source impedance on a telephone line and which assigns the measured magnitudes to a range within a number of predetermined ranges to thus form a comparison to determine if harmful conditions exist on the telephone lines.
It is a still further object of the present invention to provide a method for measuring the equivalent voltage source voltage magnitude and equivalent voltage source impedance magnitude to determine if harmful conditions exist on the telephone lines which may cause interruption of telephone service.